Forty consenting patients, women and men, 18 - 75 years old will be recruited. All subjects will have a primary diagnosis of major depression, and at the time of recruitment will be experiencing a major depressive episode with a duration ≥ 3 weeks and < 6 months. Subjects will be eligible to enter the study only if they will have a minimum score of 18 points on the 24-item Hamilton Rating Scale for Depression (HAMD) and are receiving conventional antidepressant treatment in adequate dose for at least 3 weeks with no more than mild improvement Blood cell count, liver and kidney functions will be performed before entering the study, only in patients who have not had them performed during the last 6 month prior to entering the study.